1. Field of the Invention
The present invention relates to anhydrous mirtazapine and a process for preparing the same.
2. Discussion of the Background
U.S. Pat. No. 4,062,848 discloses a process for increasing the purity of mirtazapine, (a useful antidepressant), by recrystallizing mirtazapine from a petroleum ether or similar subject.
However, in performing this process, impurities are precipitated in an oily state when crude mirtazapine having a purity of about 95 to 99% is used, so that the crystallization of mirtazapine is inhibited, and makes it difficult to crystallize mirtazapine having a high purity.
Accordingly, there is a significant need for a process capable of efficiently and industrially preparing anhydrous mirtazapine having a high purity from crude mirtazapine.
Accordingly, one object of the present invention is to provide a process capable of efficiently preparing an anhydrous mirtazapine crystal substantially free of lower alcohol insolubles.
A further object of the present invention is to provide a method for the production of anhydrous mirtazapine having an average particle diameter of 10 to 50 xcexcm and substantially free of residual solvent.
These and other objects of the present invention have been satisfied by the discovery of a process for preparing an anhydrous mirtazapine crystal, comprising filtering a lower alcohol solution of crude mirtazapine to provide a filtrate; concentrating the filtrate to provide a concentrated filtrate; and crystallizing anhydrous mirtazapine from the concentrated filtrate using a precipitation solvent selected from the group consisting of heptane and petroleum ethers and the anhydrous mirtazapine crystal produced thereby which is substantially free of lower alcohol insolubles.
In a further embodiment, the present invention relates to the discovery of a process for the production of anhydrous mirtazapine crystal that is substantially free of residual solvent, by pulverizing the anhydrous mirtazapine to an average particle diameter of from 10 to 50 xcexcm, and the anhydrous mirtazapine crystal produced thereby.